About Rumpelstiltskin // Headcanon
Jefferson actually worked for Rumpelstiltskin from his teenage days, around 17 to the moment he lost Alice, around his 31, 32.
The hatter always had mixed feelings for his employer. It was something between rightful fear and fascination, self destructive attraction and respect, scared obedience and something actually close to friendship.
He used to call him "my lord", the only man he never shortened the title with. If he crossed the Dark One's path in Storybrooke, he would definitely had this old habit to come back.
Rumpelstiltskin was the one who taught him all the hatter knows about magic theory (as he never achieved to work any kind of spell).
When he was young, Jefferson admired the Imp and spent so much time around him that he seemed to unintentionally mimic his master's manners, using "dearie" as a pet name for a lot of people, developing a habit of giggling at random times.
Jefferson could spend hours sat on a window frame, simply listening to Rumpelstiltskin spinning. Sometimes the hatter sang for him songs of the many lands he'd visited.
He knew about Belle even though he never got to meet her before the curse.
In the end, in a strange kind of way, Jefferson liked his employer as much as he feared him.